The
technique, which takes two years to achieve, gives scientists another option
for capturing and storing the excess CO2 humans are pumping
into the atmosphere – and could one day be scaled up to take
significant levels of carbon out of circulation.

The
research was conducted by a team from the the US Department of Energy's Pacific
Northwest National Laboratory (PNNL), and builds on a
similar experiment in Iceland earlier this year, which dissolved CO2
in water and injected it into a basalt formation.

In
the latest study, undiluted CO2 was used, and much more of it was stored at
once: 1,000 tonnes of fluid carbon dioxide. The
PNNL team had already shown that the chemical reactions could
happen in lab conditions, but until now, they didn't know how long the
reactions would take in a real-world setting.

"Now
we know that this mineral trapping process can occur very quickly, it makes it
safe to store CO2 in these formations," says researcher Pete McGrail.
"We know now that in a short period of time the CO2 will be permanently
trapped."

In
their field study, the researchers injected the fluid carbon dioxide into
hardened lava flows some 900 metres (2,952 feet) underground, near the town of
Wallula in Washington State. At
that depth, minerals including calcium, iron, and magnesium make up part of the
basalt formations. These minerals become unstable, and then dissolve in the
acidic conditions created by the CO2.

The
dissolving minerals react with the carbon dioxide to form the carbonate
material ankerite,
which is similar to limestone,
and binds with the basalt. You
can see the end results marked by the white areas in the sample shown in the
image above. While
turning CO2 into rock isn't
a new idea, scientists are working
to make the process quicker and more efficient – as original estimates predicted the
reactions could take thousands of years.

Basalts
are found all around the world, including North America and Iceland, which is
one of the reasons the technique could be an effective way of dealing with
excess CO2.

But
before we get too excited about sending all of our excess carbon underground,
there are still some issues to resolve. Capturing
carbon remains
relatively expensive, and scientists aren't sure how well these experiments
will ultimately scale up, particularly as more and more existing basalt
formations turn into carbonate.

Then
there's the question of accurately gauging how much storage capacity the basalt
actually offers. Scientists
have recently found that our calculations of another carbon storage method –
soil's natural capacity to absorb and store CO2 – had been overestimated by
as much as 40 percent. So
we need to wait for further tests to be carried out before declaring all
our carbon worries over, but it's a promising area of research, and it gives us
an end result that's difficult to beat: CO2 in a safe and solid form deep below
the ground, where it can't do any harm to the
atmosphere or oceans.

"[The
CO2] can't leak, there's no place for it to go, it's back to solid rock," explains McGrail.
"There isn't a more safer or permanent storage mechanism."